We used the aerosol particles sampled during the Lindenberg Aerosol Characterization Experiment 1998 (LACE 98) to study the influence and importance of particle morphology, composition, and internal structure of mixed particles on light scattering and absorption. The focus lay on particles with mixed composition, i.e., of soot and ammonium sulfate as components. The single particle analysis of the aerosol particles was performed with an high resolution scanning electron microscope and a transmission electron microscope. The calculations of scattering and absorption of light by these particles were done with the Fortran code DDSCAT. The most important particle properties for the optical parameters of mixed soot-sulfate particles are the volume content of the absorbing soot component and the refractive index, i.e., the imaginary part of the soot inclusions. The internal arrangement of the inclusions and the morphology of the particles are of minor importance. With the particle compositions and size distributions from aerosols collected during the LACE 98 field campaign, the influence of the mixed soot/sulfate particles on the optical properties of these aerosols were studied. The size distribution, the internal or external mixing state of the particles and the soot content in the mixed soot/ sulfate particles have the strongest influence on the aerosol optical properties.